Strange electrical problems

I have a 2004 Jetta 1.8t manual transmission. This problem does not happen every time I drive, but enough to be really annoying. The main issue is that when I park and shut the car off the clock and trip odometer reset and the radio shuts off with the key still in the ignition. It seems to be more frequent when I have had the AC on, I have tried shutting it off before turning off the ignition, but it still happens. At times when my dash lights are on they will dim as well as my head lights while driving. Occasionally the car will die when stopped and everything electrical shuts off, but there is no problem starting the car right away. While driving the car will bing 3 times, but there is no warning light to go along with the bings. The auto windows will not always raise/lower the window with a single push but there is no problem if you hold down on the button. With the dash lights on lowering the window has caused the dash/headlights to dim. I have checked the battery and alternator they both test just fine and took it to the dealership and they could not find anything. The car has 49100 miles on it so my warranty is just about up and would like to figure this out before I have to pay anything. Any help would be greatly appreciated

Thanks